1. Field of the Invention
The present invention relates generally to pulsed lasers, and more particularly, to discharge stabilization of high repetition rate lasers.
2. Description of Related Art
The assignee of the present invention has developed TEA CO.sub.2 lasers that provide high repetition rate (to 200 Hz) output in a compact, sealed package using a catalyst. However, this compact, sealed, high repetition rate TEA CO.sub.2 laser, and other such pulsed lasers that utilize a catalyst, suffer from discharge arcing in the first several shots just after turn-on from a quiescent state. The quiescent state may be as short as tens of seconds. Arc elimination is important for laser lifetime and to guarantee "first shot" capability in a high data rate situation. Heretofore, no means or method of suppressing initial arcing has been available.
High repetition rate TEA CO.sub.2 lasers produce laser output by pumping a gas mixture with a high power electrical discharge that takes place between two accurately aligned and surfaced electrodes. Lasers of this type that operate sealed with a catalyst have the problem that when they are first turned on, discharge arcing occurs for the first several shots. These arcs are highly localized current paths that prevent laser emission and cause inordinate wear of the electrodes, with the danger of permanent electrode damage under similar repeated use. However, the initial arcs do generate preionizer species that stabilize subsequent discharges.
The problem of initial shot arcing has been associated with high repetition rate (200 Hz) lasers that are compact, with relatively small gas ballast, and that operate sealed with a heterogeneous catalyst. In these lasers, neutral, low ionization potential hydrocarbons that are necessary for discharge stabilization are attached by the catalyst. The initial arcs produce low ionization potential species from the main gas constituents that replace the hydrocarbons. For very large lasers, operating at reduced repetition rates on the order of 20 Hz, initial shot arcing has generally not been a problem, but it is not yet known if the quality of laser output could be enhanced using the auxiliary discharge concepts of the present invention.
Heretofore, a primary auxiliary discharge located adjacent to the electrodes has been used to preionize low density hydrocarbons that then act as a uniform background for stabilization of the main voltage pulse. This auxiliary discharge is used as a preionizer that creams a low density of charged particles in the main discharge volume to act as a uniform seed for the main voltage pulse. However, this auxiliary discharge has not eliminated the occurrence of the initial arcs, whose overall effect is to deteriorate the laser, impair its performance, and limit its operating lifetime.
Accordingly, it is an objective of the present invention to provide for a method and apparatus that eliminates the above-described discharge arcing problem in pulsed high repetition rate lasers, and the like. It is a further objective of the present invention to provide for a method and apparatus that provides ionizable species having low ionization potential derived from a secondary auxiliary discharge.